Lego Lamborghini Sian Gearbox Problems

The LEGO Technic line is lauded for its engineering marvels, and the Lamborghini Sian is among its standout models. However, a number of enthusiasts have noted concerns with its gearbox assembly.

The Problem:

Upon assembly, some users have identified that the gears in the Sian’s gearbox do not turn smoothly. The gears, when unattached, seem to function with ease, especially in the lower gears. But the moment the gearbox is connected to the rear differential, the gears tend to “jump” or emit a grinding noise. This discrepancy is particularly notable when contrasted with the sound and functionality of gears in the LEGO Bugatti Chiron, which many have mentioned to be notably smoother.

Potential Solutions:

Here’s a summary of the potential fixes, drawn from the experiences of LEGO enthusiasts:

1. 20-tooth Tan Bevel Gears: One suggestion is to swap or flip the 20-tooth tan bevel gears. There’s been mention of these particular gears causing some issues. Along with this, it’s crucial to ensure that the differential spider gears are in proper working order.
2. Neutral Gear Realignment: If the grinding is observed even in reverse, one remedy might be to switch gears, put it in neutral, then switch the gears again. Rolling the car forward a bit can sometimes help to release any built-up friction caused during the assembly process.
3. Differential and Orange Wave Selector Positioning: It’s essential to ensure that the differentials are facing the correct way and that the orange wave selectors are correctly inserted.
4. Wiggle Room for Gears: An overlooked yet crucial aspect is that the gears should have some wiggle room on the axle. If they’re too tight or right against another part on the axle, this can create significant friction, hampering their smooth movement.
5. Defective Beige Gears: Some have discovered that the beige 20-tooth bevel gears might be defective. Swapping these gears from another set or ordering replacements from LEGO can improve the situation. It’s essential to inspect the beige gears for irregularities.
6. Instructional Discrepancies: It’s worth noting that there may be occasional errors or discrepancies in the LEGO instruction booklet. Always double-check the assembly instructions and cross-reference with other reliable sources if needed.
7. Red Piece Alignment in Assembly: A specific step to look out for is step 81-3 on page 69 of book 1. During this step, the red piece added must fit correctly around the differential. If not, when you progress to step 117 on page 88, the red piece might be pushed over, causing misalignment. Ensure everything remains aligned during assembly to prevent any binding.

In conclusion, while the LEGO Lamborghini Sian is a marvel in design and intricacy, there might be hitches along the way during assembly, especially concerning the gearbox. But with a bit of patience, troubleshooting, and the above-mentioned solutions, a smooth-running model is within reach. As with any LEGO project, the joy often lies as much in the journey of building as it does in the finished product. Happy building!